| A | B |
|---|
| nucleus | The central core of an atom containing protons and usually neutron. |
| proton | Small, positively charged particle in the nucleus of an atom. |
| neutron | Small uncharged particle in the nucleus of an atom. |
| electron | A tiny, negatively charged, high-energy particle that moves in the space outside the nucleus of an atom. |
| atomic number | The number of protons in the nucleus of an atom. |
| atomic mass unit (amu) | A unit of measurement for the mass of particles in atoms. |
| valence electron | The electrons that are farthest away from the nucleus of an atom and involved in chemical reactions. |
| electron dot diagram | A representation of the number of valence electrons in an atom, using dots placed around the symbol of an element. |
| atomic mass | The average mass of one atom of an element. |
| periodic table | An arrangement of the elements in order of atomic number, in which elements with similar properties are grouped in columns. |
| group | Elements in the same vertical column of the periodic table; also called a family. |
| family | Elements in the same vertical column of the periodic table; also called a group |
| period | A horizontal row of elements in the periodic table. |
| malleable | A term used to describe material that can be pounded or rolled into shape. |
| ductile | A term used to describe a material that can be pulled out into a long wire. |
| conductor | A substance through which electrons move freely, transmitting heat or electricity. |
| magnetic | A characteristic of those metals that are attracted to magnets and can be made into magnets. |
| alkali metal | An element in Group 1 of the periodic table. |
| alkaline earth metal | An element in Group 2 of the periodic table. |
| transition metal | An element in Groups 3 through 12 of the periodic table. |
| lanthanide | A group of elements in the first row of the rare earth elements in the periodic table. |
| actinide | A group of elements in the second row of the rare earth elements in the periodic table. |
| nonmetal | An element that lacks most of the properties of metals. |
| diatomic molecule | A molecule composed of two atoms. |
| halogen family | The elements in Group 17 of the periodic table. |
| noble gas | An element in Group 18 of the periodic table. |
| metalloid | An element that has some of the characteristics of metals and some of the characteristics of nonmetals. |
| semiconductor | A substance that can conduct electricity under some conditions. |
| atom | Basic unit of a chemical element. |
| element | A substance that cannot be broken down into other substances by chemical or physical means. |
